WASHINGTON (Reuters) - The United States should deploy ships, step up covert activities and sharpen its rhetoric to make more credible the threat of a U.S. military strike to stop Iran’s nuclear program, a bipartisan group said on Wednesday.

Former U.S. politicians, generals and officials said in a report that the best chance of stopping Iran’s suspected pursuit of nuclear weapons was to make clear American willingness to use force, although it stopped short of advocating military action.

The report by a Bipartisan Policy Center (BPC) task force of Democrats, Republicans and independents is to be formally issued on Wednesday and comes amid speculation about the possibility of an Israeli military strike against Iran.

There is little evidence to suggest that U.S. President Barack Obama has any significant interest in the possibility of a military strike against Iran, though his administration has repeatedly said that all options are on the table.

To a lesser degree there has also been debate about a U.S. attack, an idea advocated by former Pentagon defense planner Matthew Kroenig in his recent Foreign Affairs Magazine article, “Time to Attack Iran: Why a Strike Is the Least Bad Option.”

The BPC report’s central thesis is that to persuade Iran to address questions about its nuclear program via negotiations, economic sanctions must be accompanied by a credible threat of military attack against Iran’s nuclear facilities.

“The United States needs to make clear that Iran faces a choice: it can either abandon its nuclear program through a negotiated arrangement or have its program destroyed militarily by the United States or Israel,” said the report, entitled “Meeting the Challenge: Stopping the Clock.”

CREDIBLE THREAT

Tensions between Iran and the West have grown as the United States and its European allies have tightened economic sanctions by targeting the oil exports that drive the Iranian economy.

The United States, and many of its European allies, suspect that Iran is using its civilian nuclear program as a cover to develop the atomic bomb. Iran denies this, saying that its program is solely for civilian uses such as power generation.

The BPC is a nonprofit policy group founded by prominent Republicans and Democrats that seeks to promote policy-making that can draw support from both major U.S. political parties.

The task force members include Chuck Robb, a Democrat and former U.S. senator from Virginia; Mortimer Zuckerman, a real estate mogul, publisher and long-time Democratic Party backer; John Hannah, national security adviser to former Vice President Dick Cheney, and Eric Edelman, a career diplomat who served at the Pentagon under former Defense Secretary Donald Rumsfeld.

Among its specific recommendations, the report calls for:

- strengthening the United States “declaratory policy” to make clear its willingness to use force rather than permit Iran to acquire nuclear weapons;

- bolstering the presence of the U.S. Fifth Fleet in the Gulf and the Gulf of Oman by deploying an additional carrier battle group and minesweepers off Iran, conducting broad military exercises in the region with allies, and prepositioning supplies for the possibility of military action against Iran;

- strengthening the ability of U.S. allies such as Saudi Arabia, the world’s largest oil exporter, to ship oil out of the region without using the Strait of Hormuz, which Iran has threatened to close in retaliation for Western sanctions;

- and amplifying U.S. efforts to strengthen the militaries of countries in the region such as Saudi Arabia, Kuwait, Oman and the United Arab Emirates through arms sales.

Should these steps fail to dissuade Iran from its suspected pursuit of nuclear weapons, the report urges the United States to consider a “quarantine” to block refined petroleum imports by Iran, which is heavily dependent on gasoline refined abroad.

As a last resort, the group asserts that the U.S. military has the ability to launch “an effective surgical strike against Iran’s nuclear program.”

DISENTANGLE THE U.S. MILITARY

Obama’s broader foreign policy has sought to disentangle the U.S. military from its commitments in the Muslim world. He decided to withdraw all U.S. troops from Iraq last year and aims to wind up the U.S. combat mission in Afghanistan in 2014.

Obama opposed his predecessor George W. Bush’s 2003 invasion of Iraq, a decision the Bush administration chiefly justified by citing intelligence that Iraq had weapons of mass destruction. No such weapons were subsequently found.

Without explicitly calling for an attack on Iran, the report says such a strike would include an air campaign of several weeks to target key military and nuclear installations, accompanied by the U.S. special forces on the ground.

“A military strike would delay Iran’s acquisition of nuclear capability but not eliminate it,” the report said.

“Still, policymakers need to consider whether delaying Iran’s program in the short term would allow Washington to take advantage of that space to stop Iran’s nuclear program altogether,” it added without explaining how this might happen.

“It is also possible that the delays and increased costs that a devastating strike would impose on Iran’s nuclear program might be followed by a different set of dynamics that would cause or compel the Iranian leadership to change course,” it said.

The report acknowledged a strike would carry many risks, including higher oil prices, possible Iranian retaliation against U.S. military installations, support of “terrorist” operations against U.S. interests and potential attacks on Iraq.

Robb, who co-chaired the task force, told Reuters the group chose not to explicitly advocate military action in part because it did not want to turn what he described as a “reasoned, thoughtful approach into, ‘This is bombs away.'”

Having repeatedly said that a nuclear-armed Iran would be unacceptable to the United States, Robb said that to be unwilling to take military action would undercut U.S. credibility.

“Our credibility is very much on the line,” he said. “We believe that we have to be credible with respect to the kinetic option. We need to provide evidence that we are preparing to take that option if necessary.”